High temperature electron discharge device and apparatus



J. E. BEGGS 3,050,651

HIGH TEMPERATURE ELECTRON DISCHARGE DEVICE AND APPARATUS Aug. 21, 1962 Filed Sept. 4. 195 6 Fig. 4.

Plate Voltage P/ale Voltage Fig. 8.

lnvenfor: James E Begggs,

His Attorney- Patented Aug. 21, 1962 3,050,651 IHGH TEMPERATURE ELECTRON DISCHARGE DEVIQE AND APPARATUS James E. Beggs, Schenectady, N.Y., assignor to General Electric tlompany, a corporation of New York Filed Sept. 4, 1956, er. No. 667,805 Claims. (til. 313-) My invention relates to high temperature electron discharge devices and apparatus and particularly to such apparatus capable of operating at ambient temperatures of the order of 400800 C.

As electronic equipment has become more complicated and larger and larger numbers of components have been required in a relatively small space as part of a complicated equipment, the problems of adequately cooling the apparatus in order to insure reliable operation have increased and many times present the limiting design problem. In accordance with an important aspect of my invention, I provide system components which are capable of operating at high temperatures and then enclose these components including electric discharge devices in a temperature-controlled enclosure and utilize the heat generated by the components to maintain the electron discharge devices at operating temperature. In this way, the problem of cooling or refrigerating is totally eliminated and the requirement for any external heating power may be eliminated from all but the starting period. In addition, all of the components actually function over a very narrow temperature range and the necessity for maintaining substantially constant characteristics over a wide temperature range or for compensating for these temperature changes is eliminated.

It is particularly advantageous in the operation of electron discharge devices, including a control member, to operate the entire device at an elevated temperature so that any uneven expansion of the parts which would otherwise tend to change the cathode-control grid spacing, for example, does not exist. In like manner, changes in tension of the grid Wires due to differences in expansion of the grid support and grid wires, is eliminated.

In accordance with an illustrated embodiment of my invention, I provide an electric discharge device of the triode type which is particularly suited for high temperature operation and which is made without a heater element for the cathode. A device of this character, together with suitable circuit components, to produce an operative circuit, such as a multivibrator in the illustrated embodiment, is housed in an enclosure or cabinet having such a heat loss in relation to the heat normally generated by the apparatus that a temperature in the desired operating range is attained under conditions of maximum ambient temperature without the addition of heat. Under other conditions the deficiency is made up by a simple heater supply to the enclosure itself which may be an ordinary resistance heater with a thermostatic control.

In accordance with another feature of the invention, the control grid has a titanium surface so that it is kept clean and exhibits a high work function. in this way a positive contact potential between the control grid and cathode is realized and the utilization of the device without a negative biasing circuit for the conrol member provides further circuit simplification which is of particular advantage in high temperature applications. Objects and advantages of my invention, in addition to those already discussed, will become more apparent as the following description proceeds and its scope will be pointed out in the appended claims.

In the drawing:

FIG. 1 is an elevational view in section of a triode type of heaterless electric discharge device embodying my invention;

FIG. 2 is a modified form of triode discharge device;

FIG. 3 is a diode type of discharge device which may be used in a temperature-controlled enclosure in accordance with my invention;

FIG. 4 illustrates schematically a multivibrator circuit;

FIG. 5 is a perspective view, partially broken away, illustrating the circuit of FIG. 4 in an actual physical embodiment housed within a temperature-controlled enclosure;

FIG. 6 illustrates the plate-current platevoltage characteristics of a discharge device of the type shown in FIG. 3 at different operating temperatures;

FIG. 7 represents the plate-current plate-voltage characteristics of a triode for different values of grid voltage;

FIG. 8 illustrates the grid-current grid-voltage characteristics showing the positive contact potential, and

FIG. 9 schematically illustrates a single-stage audioarnplifier exhibiting positive contact potential between grid and cathode.

Referring now to FIG. 1 of the drawing, the discharge device there shown is of the disk-seal type in which the anode, grid and cathode terminals 1, 2 and 3 form a part of the evacuated envelope which is completed by the hollow cylindrical ceramic spacers 4 and 5. These spacers also function to mutually insulate terminals 1, 2 and 3. The plate electrode 6, control grid electrode 7 and the cathode electrode 8 are of the planar type and are sup ported in closely spaced relation within the envelope of the electric discharge device and electrically connected respectively with the externally accessible terminals provided by members ll3. In the illustrated embodiment, the plate 6 is provided by a disk of active metal such as titanium or zirconium and supported from an inwardly directed flange 4 at the upper end of the insulator 4 by means of a titanium sleeve 9 to which the disk 6 is bonded. As will be explained in more detail at a later point in the specification in connection with a method of fabricating a discharge device of this type, the upper end of the sleeve 9 is bonded in place and electrically connected to the terminal 1 by means of a conducting film 10 extending between the cylinder 9 and the terminal 1, and reacted with the upper surface of the insulator 4. In a similar manner, the cathode '8 may be in the form of a disk, which may be of platinum or of titanium having an overlayer of sintered material such as tungsten, molybdenum, titanium, or titanium monoxide and supported from insulator 5 by a titanium or hafnium sleeve 11 which is conductively connected with terminal 3 by conducting film 12. The upper surface of the disk in either event is coated with a suitable electron emissive material 8 such as the alkaline-earth oxide coatings which are well known in the art.

The grid electrode is in the form of a plurality of fine Wires supported from a grid washer 13. This washer, as illustrated, is received within a recess 14 formed on the inner and lower edge of the annular disk-like terminal 2 and engaged by the downward flange 14' of that terminal.

An electric discharge device, particularly well suited for operation at high temperatures in the order of 400 C. to 760 C. may be provided by utilizing titanium metal for the terminals 1-3. As previously indicated, however, a substantial amount of titanium is exposed to the interior of the envelope by virtue of the internal parts of the device which may be of titanium. These parts include the anode disk e, the foil supports 9 and 11 and the cathode disk 8.

It will be appreciated by those skilled in the art that the discharge device described in connection with FIG. 1 may be fabricated in a number of ways; however, it may be, to particular advantage, exhausted and fabricated in a single heating operation by utilizing nickel shims adjacent the titanium members for producing a bond between the ceramic spacers and the titanium members 1, 2 and 3. Such a process is described in detail and claimed in my copending application Serial No. 409,159, filed February 9, 1954, now Patent No. 2,857,663, and assigned to the assignee of this application.

In FIG. 2 is shown a very similar electric discharge device construction in which the cathode and anode electrodes are in the form of solid members supported directly from the anode-cathode terminals and corresponding parts have been designated by the same reference numerals. Where the correspondence is not complete, the reference numerals are primed. It is to be noted from inspection of FIG. 2, anode is integrally formed with the anode terminal 1' while the cathode is in the form of a solid cylindrical member 16, formed integrally with the cathode the cathode terminal 3.

In FIG. 3 is shown an elevational view in section of a diode type of discharge device. This device is the same as the cathode end of the discharge device shown in FIG. 1 and with the upper part of the envelope removed and the grid electrode replaced by an anode disk 17, preferably of titanium, which is bonded directly to the cathode supporting insulator 5.

As an illustration of a type of circuit which may readily be produced out of high temperature components, including electric discharge devices of the type described, there is shown schematically in FIG. 4, a free-running multivibrator circuit, including electric discharge devices 18 and 19, each including a cathode 20, a control grid 21 and an anode 22. The anode-cathode circuits of these discharge devices are connected in parallel between a conductor 23 which is for connection to a positive source of direct current and a conductor 24- which may be operated at ground. The anode-cathode circuits are completed through anode resistors 25 and 26 respectively. As will be readily appreciated by those skilled in the art, the grid-cathode circuit of the discharge device 18 includes a resistor 27 and the grid-cathode circuit of discharge device 19 includes a resistor 28. The anode of discharge device 18 is connected to the grid of discharge device 19 through a capacitor 29 and similarly the anode of discharge device 19 is connected with the grid of discharge device 18 through a capacitor 30. The output of the circuit may be conveniently taken from the anode terminal of discharge device 1? through conductor 31. It will be readily appreciated by those skilled in the art that conductivity of discharge device 18, for example, increases as i the conductivity of discharge device 19 decreases and vice versa to produce, from the direct current voltage impressed on conductor 23, a voltage which may be of rectangular wave shape or substantially sinusoidal wave shape and which has a periodicity depending upon the time constants of the circuits associated with discharge devices 18 and 19.

In FIG. 5 is shown an actual physical embodiment of my invention in which the circuit just described in conneotion with FIG. 4, utilizing high temperature components including electric discharge devices of the type shown in FIG. 1, mounted upon a suitable panel board and housed within an enclosure, the temperature of which is regulated to a value at which the electric discharge devices will operate.

Referring now particularly to FIG. 5 of the drawing, the components making up the circuit schematically shown in FIG. 4 are mounted on a panel board 32 which may be of any insulating material capable of withstanding high temperatures and may to advantage be formed of ceramic material. The circuit elements corresponding to the tubes 18 and 19, capacitors 29 and 30, and resistors 7 printing techniques which are suitable for high tempera ture operation and may to advantage be formed by the method described and claimed in my copending application Serial No. 464,080, filed October 22, 1954 and assigned to the assignee of this application. In accordance with one embodiment of the method there described and claimed, the conducting paths are established by painting the surface with powdered titanium hydride and powdered nickel in a suitable carbonaceous compound, such as one of the nitrocellulose fugitive binders, and subsequently heating in vacuum until the hydride is dissociated and the painted paths metalized by an adhering metal film.

The enclosing casing 3 is shown as made up of a body part 33 and the cover 34. It is contemplated that the temperature within the device will be maintained essentially by the heat generated in various components once normal operating conditions are established. However, in order to bring the enclosure to operating temperature, during starting up, and also to permit some variation in the ambient or load conditions under which the circuit operates, the circuit and enclosure are designed so that the operating temperatures would, in the absence of any heat supply means in addition to the normal circuit components, be a little less than that deSired.- Then the additional heat is supplied by a resistance heater element illustrated schematically at 3:5. The energization of the heater element 35, from electric supply conductors 36, is controlled by a thermostatic device illustrated schematically at 37.

The positive direct current supply for the multivibrator circuit conductor is designated by numeral 23' corresponding to the conductor 23 of FIG. 5, the ground conductor by numeral 24' and the output conductor by numeral 31'.

The operation of heaterless electric discharge devices in accordance with my invention may be better understood by a brief consideration of the characteristic curves shown in FIGS. 6 and 7. In FIG. 6, the plate-current plate-voltage characteristics for a diode such as shown on FIG. 3 are shown for operating temperatures ranging from 400 to 700 C. It will be seen that the current per square centimeter of cathode area increases about tenfold for each rise in temperature within this range. It is apparent from a consideration of these curves that the total emission current for a desired operating temperature may be established at a desired value by fixing the area of the emitter accordingly. Thus a one square centimeter emitter operated at 500 C. Will give a saturation current in the order of 10 milliamperes and readily permit operation with an average plate current in the order of 5 milliarnperes. The triode characteristic of discharge devices such as shown in FIGS. 1 and 2 is illustrated in the curves of FIG. 7. The curves are taken for grid voltage variations of .5 volt and the characteristics shown are for a range of grid voltages from 3.5 volts to +3.5 volts.

Another and important aspect of the present invention resides in providing electric discharge devices having a positive contact potential between the grid and cathode of a triode or between the anode and cathode in a diode. In electric discharge devices of conventional construction, a negative voltage on the grid of a triode is required to prevent the drawing of substantial grid current. This is due to the moderately low work function of the grid after the tube has been in operation and this in turn results from a certain amount of surface contamination of the grid surface by materials evaporated from the cathode. The grid thus tends to become an emitter of electrons. There are two aspects of the present invention which eliminate this undesirable tendency of the grid to emit and as a result provide a discharge device having a positive contact potential between the grid and cathode of something like 2.0 volts, for example. In the first place, the grid or at least the surface of the grid is composed of a material, specifically titanium, which tends to reduce any compounds, such as oxides deposited thereon from the cathode. When the grid operates at a high temperature in accordance with the method of the present invention, the residual ma terial such as barium is re-evaporated to leave the grid essentially clean. While the grid wires themselves may be made of titanium; tungsten, for example, is a much better material structurally and so in a preferred embodiment, the actual grid wires are tungsten on which the surface layer of titanium has been applied in any suitable way, as by evaporation. The magnitude of the positive contact potential is determined in part by the effectiveness of the grid in keeping itself clean and hence of a high work function. If the cathode has a very active base metal and tends to give off a substantial amount of material, it may be necessary to run the grid at an even higher temperature than the cathode to maintain the positive contact potential in the order of 2.0 volts. However, for a cathode with a moderately passive base metal, operating the entire device at the same temperature and with a titanium surface on the grid, or on the anode in the case of a diode, a positive contact potential in the order of 2.0 volts is realized. With a very passive cathode the positive contact potential may be maintained with the grid at a temperature somewhat less than that of the cathode.

In FIG. 8 this positive contact potential between the control member and cathode is illustrated by the grid current-grid voltage curve taken with both the control grid and cathode at 450 C. The particular discharge device exhibiting this characteristic had a tungsten wire grid with a titanium surface and an oxide cathode of a relatively passive type including a support of platinum for the oxide coating.

In accordance with the foregoing description, it is a particular advantage that the temperature of the control grid may be made the same as that of the cathode and may be accomplished by utilizing a heaterless discharge device in a compartment maintained at a desired operating temperature for the entire device. It is also possible to realize the positive contact potential by utilizing the materials mentioned and maintaining the temperature of the control grid by a separate source of heat.

This operation of electric discharge devices with a stable positive contact potential is of great significance in high temperature applications. It permits the elimination of biasing resistor-capacitor networks or batteries. In FIG. 9 there is illustrated a trio-de amplifier exemplifying the circuit simplicity that may be realized with a discharge device having a positive contact potential. The discharge device which may be of a structure such as shown in FIG. 1 includes an anode 38, a control grid 39 and a cathode 40. In accordance with the features of the invention just described, the control member or at least the surface thereof, is formed of titanium. The cathode is coated with an oxide coating and preferably includes a support of relatively passive material such as platinum. The discharge device as a whole is enclosed within a temperature-control cabinet indicated by the dotted outline 41. The starting temperature of the device may be attained by auxiliary heating means illustrated as a resistance heating element 42 energized from a source of alternating voltage 43 under the control of a thermostat 44. Since the discharge device has a positive contact potential, no grid bias is required and the input circuit may be connected directly to a signal source which may be a barium titanate phonograph pick-up illustrated diagrammatically at 45. The output from the anode-cathode circuit is supplied to the primary winding 46 of an output transformer 47, secondary winding 48 of which is connected to energize a loud speaker illustrated diagrammatically at 49. The anode-cathode circuit is completed through a plate supply by battery Sll.

This amplifier, with no biasing circuit connected to the input or grid electrode, may be operated within the enclosure at 500 C. and not draw any grid current even though the peak alternating grid voltage becomes positive as much as 2 plus volts.

From the foregoing description of a number of embodirnents of my invention, it is apparent that I have provided discharge devices having superior properties with respect to high temperature operation. These devices may also exhibit a positive contact potential, that is, a positive contact potential between the control grid and the cathode of a triode or between the anode and cathode of a diode. The invention further involves a simplification of apparatus and the elimination of the cooling or refrigeration problem of electric discharge device and component apparatus.

While I have described particular embodiments of my invention, it will be apparent to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects and I aim therefore in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Electron discharge apparatus comprising an electron discharge device including an anode, a control grid and a heaterless thermionically emissive cathode enclosed within an evacuated envelope including a body of titanium exposed to the interior thereof, circuit components connected with the electrodes of said electric discharge device, an enclosing casing surrounding said discharge device and components and a heater element for supplying heat to the interior of said casing to supplement the heat generated by operation of said discharge device and components to maintain a predetermined level of emission from said cathode.

2. An electron discharge device comprising a vacuumtight envelope providing a plurality of mutually insulated terminals, a control grid within said envelope connected to one of said terminals and including a surface coating of titanium and a cathode spaced from said grid within said envelope and connected with another of said terminals, and an anode spaced from said grid and connected to a third one of said terminals, said cathode having an oxide coating, means maintaining said grid at an elevated temperature during operation of said device to maintain said grid free of oxide from said cathode and thereby to maintain a high work function and provide a positive contact potential between said control grid and said cathode.

3. An electron discharge device comprising an envelope including a plurality of metal disk-like terminals, a plurality of hollow cylindrical ceramic insulators interposed respectively between successive terminals, a control grid within said envelope connected to one of said terminals, and including a surface coating of titanium and a cathode spaced from said grid within said envelope and connected with another of said terminals, said cathode having an oxide coating, means maintaining said grid at an elevated temperature during operation of said device to maintain said grid free of oxide from said cathode and thereby to maintain a high work function and provide a positive contact potential between said control grid and said cathode.

4. An electron discharge device comprising an envelope including a plurality of metal disk-like terminals, a plurality of hollow cylindrical ceramic insulators interposed respectively between successive terminals, a control grid within said envelope connected to one of said terminals, and including a surface coating of titanium and a cathode spaced from said grid within said envelope and connected with another of said terminals, said cathode having an oxide coating, and means maintaining said grid and said cathode at substantially the same temperature whereby said grid maintains itself free of oxide from said cathode during operation of said device to maintain a high work function and provide a positive contact potential between said control grid and said cathode.

5. An electron discharge device comprising an envelope including a plurality of metal disk-like terminals, a plurality of hollow cylindrical ceramic insulators interposed respectively between successive terminals, a control grid within said envelope connected to one of said terminals and including a surface coating of titanium and a heaterless cathode spaced from said grid within said envelope and connected with another of said terminals, said cathode having an oxide coating, and means external of said device for maintaining the temperature of said control grid and said cathode at a temperature in the order of 400 C. to 800 C. whereby said grid maintains itself free of oxide from said cathode during operation of said device to maintain a high work function and provide a positive contact potential between said control grid and said cathode.

6. An electron discharge device comprising an envelope including a plurality of terminals separated by a plurality of insulators, a plurality of electrodes connected respectively with said terminals including a cathode haVing a thermionically emissive coating, an electrode spaced from said cathode and including a surface of titanium and means maintaining said cathode and said other electrode at substantially the same temperature during operation of the device so that said other electrode is maintained free of emissive coating from said cathode during operation of the device and a high work function thereby provided for the surface of said other electrode and a positive contact potential maintained between said other electrode and said cathode.

7. An electron discharge device system including a discharge device having a heaterless thermionic cathode contained in a sealed, evacuated enclosure, a second electrode having a titanium surface in said enclosure and being spaced from said cathode, means for maintaining the interior of said enclosure and the entire discharge device at such a temperature as to provide a predetermined level of thermionic emission of said cathode, whereby the second electrode is maintained free of emissive coating from said cathode to establish and maintain a high work function at the surface of said second electrode relative to said cathode providing a positive contact potential between the second electrode and cathode.

8. An electron discharge device system including a discharge having a heaterless thermionic cathode contained in a sealed, evacuated enclosure, a titanium anode electrode in said enclosure spaced from said cathode and a titanium grid interposed between said anode and cathode, means for maintaining the interior of said enclosure and the entire discharge at a predetermined temperature to establish a level of thermionic emission for said cathode whereby said grid and anode are maintained free of emissive coating from said cathode to establish and maintain a high work function at the surface of said grid relative to said cathode providing a positive contact potential between the grid and cathode.

9. An electron discharge device circuit including a high vacuum discharge device having a heaterless thermionic cathode contained in a sealed, evacuated enclosure, an anode electrode spaced from said cathode and circuit elements including resistors and capacitors interconnecting said cathode and anode, means for establishing the interior of said enclosure and the entire circuit and discharge device at a predetermined temperature to establish a level of thermionic emission for said cathode, the heat dissipation from the electron discharge in said device and in said circuit elements maintaining the temperature in said enclosure at said predetermined level whereby said anode is maintained free of emissive coating from said cathode to establish and maintain a high work function at the surfaces thereof relative to said cathode to provide a positive contact potential between the anode and cathode.

10. Electron discharge apparatus comprising an electron discharge device including an anode, and a heaterless thermionically emissive cathode enclosed within an evacuated envelope including a body of titanium exposed to the interior thereof, circuit components connected with the electrodes of said electric discharge device, an enclosing casing surrounding said discharge device and components and a heater element for supplying heat to the interior of said casing to supplement the heat generated by operation of said discharge device and components to maintain a predetermined level of emission from said cathode.

References Cited in the file of this patent UNITED STATES PATENTS 1,839,899 Slepian Jan. 5, 1932 2,189,618 Slepian et al. Feb. 6, 1940 2,367,331 Bondley Jan. 16, 1945 2,493,659 Dorgelo Jan. 30, 1950 2,609,518 Klopping Sept. 2, 1952 2,754,445 Sorg July 10, 1956 2,846,609 Espersen Aug. 5, 1958 FOREIGN PATENTS 535,505 Belgium Aug. 8, 1955 

